1. Field of the Invention
This invention relates to vehicle-mounted satellite signal receiver systems and, more particularly, to a vehicle-mounted satellite signal receiving system which has a function of making up for a sensitivity error drift appearing in a satellite tracking gyro output signal.
2. Description of the Prior Art
Vehicle-mounted satellite signal receiving systems have heretofore been developed for receiving electromagnetic waves from a broadcasting satellite (hereinafter referred to as BS) or a communication satellite (hereinafter referred to as CS) by tracking the BS or CS (hereinafter typically referred to as BS) with an antenna. In such a system, when receiving signals from the BS, a position or bearing of a receiving antenna corresponding to the maximum received power level of the BS signal is found by rotating the antenna, and to maintain this maximum received power level an optimum antenna position is determined by sampling power level changes obtained while slightly changing antenna beam direction or angle (this system is often referred to as a step track system).
Such a system, however, cannot be used while the vehicle is moving, as it is now impossible to receive BS waves. To solve this problem, a BS tracking system has been proposed which uses a gyro or like yaw rate sensor for detecting the yaw rate of the vehicle and tracks the BS according to vehicle bearing changes determined from the angular velocity of the vehicle detected by the yaw rate sensor.
Japanese Laid-Open Patent Publication No. Hei 4-336821 discloses a vehicle-mounted BS signal receiver, which tracks the BS by directing the antenna toward the BS with a gyro sensor under a high electric field intensity condition while directing the antenna toward the BS by making use of the received wave power level peak under a low electric field intensity condition.
Japanese Laid-Open Patent Publication No. Sho 63-262904 also discloses a vehicle-mounted BS signal receiver.
Japanese Laid-Open Patent Publication Hei 5-142321 discloses a vehicle-mounted BS signal receiver which permits angle sensor calibration to enable control of the antenna direction toward the BS, even under wave-obstructed conditions, through use of an inexpensive angle sensor.
Japanese Laid-Open Patent Publication No. Hei 6-104780 discloses a system, which, after directing a receiving antenna in the maximum received power level direction, uses a gyro sensor to maintain the antenna altitude in a fixed direction according to the movement of the vehicle.